The present invention relates to a method for producing oil or gas from a well in an oil or gas reservoir, or of injecting fluids into a well in an oil or gas reservoir. The invention further relates to a production pipe with a lower drainage pipe for use in such methods. The invention is particularly suitable for long, horizontal wells in thin oil zones in highly permeable geological formations.
Devices for recovery of oil and gas from long, horizontal and vertical wells are known from U.S. Pat. Nos. 4,821,801, 4,858,691, and 4,577,691 and GB Patent No. 2,169,018. Each of these known devices comprises a perforated drainage pipe with, for example, a filter for control of sand round the pipe. A considerable disadvantage of such known devices for oil and/or gas production in highly permeable geological formations is that the pressure in the drainage pipe increases exponentially in the upstream direction as a result of the flow friction in the pipe. Because the differential pressure between the reservoir and the drainage pipe will decrease upstream as a result, the quantity of oil and/or gas flowing from the reservoir into the drainage pipe will decrease correspondingly. The total oil and/or gas produced by such means will therefore be low. With thin oil zones and highly permeable geological formations, there is a high risk of coning, i.e. flow of unwanted water or gas into the drainage pipe downstream, where the velocity of the oil flow from the reservoir to the pipe is greater. To avoid this coning, the production rate must therefore be further reduced.
A somewhat higher production rate than that obtained by means of the known methods mentioned above can be achieved using the Stinger method, which is described in Norwegian patent application No. 902,544. Such method employs two drainage pipes, namely an outer, perforated pipe, and an inner pipe (Stinger) without perforations and which extends into the outer pipe to a desired position. The pressure profile and thus productivity achieved by means of the Stinger method are somewhat better than those achieved by other known methods. In thin oil zones with a high permeability, however, coning of unwanted water or gas may occur with this method also, resulting in reduced productivity.
The technology for drilling horizontal wells was known in 1920, but nevertheless there are many people today who regard it as pioneering technology. For the past twenty years work has been continuously in progress to develop means of drilling horizontal wells in a prudent, effective manner. The current state of technology offers high drilling safety and costs approximately 50% higher than for vertical wells. However, horizontal wells produce three to four times as much, depending on the nature of the reservoir.
It has been proven that horizontal wells are an economic necessity for recovering oil from geological formations with a thin oil zone, high permeability and in which coning of unwanted water or gas often occurs. It is anticipated that horizontal wells will be even more important in the future for exploiting small and economically marginal oil and gas fields. As well-drilling technology developed, the requirements made of reservoir drainage technology were also intensified. As described above, the known drainage technology of today has no satisfactory solutions for controlled drainage from and injection into different zones along a horizontal well.